1. Field of the Invention
This invention relates to the protection of sensitive components from hostile external environments and more particularly to an active vortex control system (AVOCS) that injects gas into a cavity to generate a vortex in front of the components to interfere with external flow fields.
2. Description of the Related Art
Components such as electro-optical (EO) sensors, optics or wafers at intermediate stages of fabrication or non-EO components (exposed because of the EO requirements) can be effected by exposure to a hostile external environment. Broadly defined, a hostile external environment is any environment that could cause a change in physical or chemical properties of the components leading to a degradation of its performance e.g. contamination, heating, erosion, ocular diffraction and distortion. The environment's external flow field interacts with the component to potentially cause the degradation. The flow field may be as benign as diffussion or outgassing in a clean room under positive pressure that may contaminate the wafers or as aggressive as an air stream in an exo-atmospheric interceptor. Physical isolation of the components from the external environment may not be cost-effective or may degrade the performance of the components depending upon the application.
Missile systems use EO sensors to acquire and track targets. The ability to accurately determine the target's position and to initiate imaging early on is critical to accomplishing the mission. Endo-atmospheric missiles experience excessive thermal loads due to the free stream air density. These systems therefore require a physical cover such as a sun shade. Once the physical cover is removed, an optical “window” can be used to protect the sensitive components from the air stream while allowing the desired wavelengths of interest to pass through unaltered. The disadvantage of such windows is that they are very expensive and thermal heating causes the window's refractive index to change during flight. This change in wave index distorts the image and causes an apparent shift in position of imaged objects. In addition, to allow multiple frequencies past the window entails significant engineering mass and manufacturing challenges. The surface heating is unpredictable and cannot be effectively compensated.
As the vehicle speed increases, the shock wave in front of the interceptor superheats the air entering the cavity to an ever greater extent. However, at larger altitudes the lower atmospheric density results in a smaller total thermal footprint. At some point, current designs reach a transition point where the added waits due to thermal heating are low enough that a nose cone can be jettisoned and the EO sensors engaged without requiring an optical window or other component protection scheme. The performance, reliability and cost associated with optical windows are such that system designers choose to delay acquisition and functional tracking by several seconds to avoid their use. The task of acquiring, identifying, tracking and intercepting an incoming ballistic missile is extremely difficult. A delay of even a few seconds of engaging the target can affect the situational awareness of the battlefield. This in turn either reduces the likelihood of a successful response or requires additional assets be deployed to ensure a successful response.